anejo 5.1 especificaciones para construcción en Áreas propensas a terremotos dia- p gasoducto

8/8/2019 Anejo 5.1 Especificaciones para Construccin en reas Propensas a Terremotos DIA- P Gasoducto

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ANEJO 5.1

Especificaciones para Construccin en reas Propensas aTerremotos


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Seismic Design Work by Gulf Interstate Engineering Company

Design Projects by GIE:

1. Reliance Pipeline (India): Design of fault crossings (2006)

2. Southwest Products Pipeline (China): Design of fault crossings (2002)

3. PG&E Gas Pipeline (California): Design of fault crossings (1991)

4. Nikiski Products Pipeline (Alaska): Design of pipeline including fault crossings (1977)

Projects which GIE Provided Seismic Design Criteria and Procedures:

1. Southwest Products Pipeline (China): Developed design criteria and procedures

necessary for the pipeline to accommodate the effects of seismic activities, includingseismic shaking, pipeline stability in liquefiable soil, landslide, and fault crossings (2002).

2. Northwest Alaska Gas Pipeline (Alaska): Developed design criteria and procedures

necessary for a Trans-Alaska gas pipeline to accommodate the effects of seismic

activities, including seismic shaking, pipeline stability in liquefiable soil, landslide, and fault

crossings (1977-1980).

Projects which GIE Reviewed and Approved Seismic Design by Others:

1. Camisea Pipeline (Peru): Design for landslides by TECHINT (2004)

2. Camisea Pipeline (Peru): Design for fault crossings by ABS Consulting (2002)

3. ENRON MetGas Pipeline (India): Design for fault crossings by ENGINEERS INDIALIMITED (2002)

4. Alyeska-Trans Alaska oil Pipeline (Alaska): Pipeline Design for seismic activities,including fault crossings, seismic shaking, and slope stability for U.S. Department ofTransportation (1976 & 1977)

Mitigation measures taken in design Pipeline in Earthquake Prone Areas:

Rerouting the pipeline to avoid the problem area.

Realigning the pipeline across a fault to ensure that the pipeline remains in tension duringany seismic activity,

Burying the pipeline in a wide ditch with long side slopes and backfilled with compactedsand to allow for lateral deformation of the pipeline alignment.

Ensuring that the pipeline has sufficient bends in the line to allow flexibility.


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Known Occurrence of Seismic Activities:

Camisea Pipeline (Peru): Sustained a 9.7 earthquake in 2007 with no damage topipeline.


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1.0 DESIGN FOR EARTHQUAKES AND GROUND DEFORMATIONSEarthquake damage to buried pipelines may be divided into two categories: (1) stress and strain

induced during transient seismic wave propagation and (2) stress and strain induced by

permanent ground deformation (PGD). Permanent ground deformations include surface faulting

and other ground movements which may be triggered by transient ground shaking during

earthquakes, including landslides on slopes, mudslides, or liquefaction of saturated sand. Faultsand landslides are likely to impose high levels of stress and strain in buried pipelines. Soil

liquefaction may cause lateral spreading of soil and/or flotation of the buried pipeline if notproperly weighted.

The principal failure modes of continuous pipelines buried at least 1 meter deep include tensilerupture and local buckling. Pipelines buried less than 1 meter deep may experience beam

buckling. Beam buckling has also occurred during post-earthquake excavation to relieve

compressive stresses

2.0 STRESS AND STRAIN CRITERIA FOR EARTHQUAKE LOADSASME B31.8 and other pipeline design standards place limits on the allowable pipe stresscaused by internal pressure and other primary design loadings, including dead loads, live loads,thermal effects and outside forces. These limits are a percentage of the specified minimum yield

strength of steel. For contingent seismic events, the pipeline may be designed based on a strain

criteria, as allowed by ASME B31.8,833.5. This criteria is intended to prevent failure of thepipe and limit unacceptable damage. Even though an earthquake or landslide may not cause the

pipe to fail, it is important to inspect the pipe for damage or deformation after such an event

before the pipeline is placed back into operation. Pipe containing unacceptable deformationmust either be repaired and/or replaced.

Pipe response to active fault movements and other seismically induced ground considers the

forces of pipe-soil interaction, large-scale deformation of pipe, and elasto-plastic pipe material.

Two failure modes are considered, tensile rupture and local buckling (wrinkling).

3.0 TRANSIENT WAVE PROPAGATION

When seismic waves travel along the ground surface, any two points located along the

propagation path will undergo out-of-phase motions. These motions induce both axial andbending strains at the pipe-soil interface of a buried pipeline. In a buried pipe the stresses due to

seismic wave propagation depend on the friction angle between the soil and pipe, the soil

subgrade modulus, seismic shear wave velocity, and the period of the earthquake wave.

Analytical studies as well as buried pipeline performance during past earthquakes have shownthat transient seismic wave propagation is unlikely to cause direct damage to modern X-grade

pipelines with quality welds. For most soils, simplified calculations will determine that stressand strain are within acceptable limits

The compression waves may cause beam buckling in a pipeline if there are sharp, small radius

bends in the pipeline and the pipe is buried less than 1 meter deep. However, buckling isunlikely to occur at the large radius field bends that are used in this pipeline.


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4.0 PIPELINE STABILITY IN LIQUEFIABLE SOIL

Ground shaking during earthquakes may cause the transformation of a saturated cohesionless

soil from a solid to a liquid. In this state, the soil behaves like a heavy fluid. This may result in

substantial deformation of the pipeline by means of buoyancy, subsidence, or loss of bearing.

For liquefaction to occur, the grain size of saturated soil must range from 0.02 mm to 2.0 mmPipeline flotation or subsidence in itself would not necessarily cause the pipeline to rupture, but

it would create service or maintenance problems. However, excess stress and strain may becaused at the locations of abrupt transition from liquefied to stable soil. Identification of areas

that will liquefy must be based on site conditions, earthquake intensity and soils drilling data.

Studies should be undertaken along the pipeline route to identify areas where liquefaction islikely to occur. The pipeline should be re-routed around these areas where possible. Where it is

not possible to avoid these areas, the design should consider the pipe stress at the transition

zones and/or modify the design to mitigate and minimize the damage that may occur. Concepts

that may be considered are as follows:

deeper burial of the pipe to a level below the liquefiable soil,

shallow burial near the transition from stable to liquefiable to reduce differential

movement,

an above ground support system with deep foundations extending into the stable soil,

soil stabilization where the extent of liquefiable soil is limited,

additional pipe weight to prevent flotation or intermittent pipe anchors to resist uplift

forces, and

installation of automatic shut-off valves on each side of the liquefiable soil area

5.0 DESIGN OF ACTIVE FAULT CROSSINGS

The characteristics of an active fault include type of fault, direction of movement, amount of

movement, and zone of influence. For example, Figure 1 demonstrates a strike-slip fault with a

horizontal displacement ( s) and a crossing angle beta ( ) less than 90 degrees. The fault

shown is a right (dextral) moving fault that will cause tension in the pipe. Note that the beta ( )angle is measured counter-clockwise from the fault line to the pipeline. If the fault were a left

(sinistral) moving fault, the configuration would cause compression in the pipe, and beta ( )angle as used in the analysis would be measured clockwise from the fault line to the pipeline

(i.e. greater than 90 degrees).

The design of each active fault crossing is based on a combination of the following elements:

1) Specify the fault crossing intersection angle beta ( ). This angle must be maintainedthrough the zone of influence and for a length greater than the length of curve on

both sides of the zone of influence.


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2) Design of a special trench configuration through the zone of influence of the fault

and for a length of the curve on both sides of the zone of influence. The trenchconfiguration is designed to facilitate the lateral movement of the pipe.

3) Control the type of backfill and compaction of backfill in the special trenchconfiguration to limit the bending strain in the pipe.

4) Control of type and compaction of backfill in the standard trench for the total

affected length on each side of the zone of influence. This controls the axial soilrestraint of the pipe to allow elongation over the full affected length and thus reduce

the total percent of axial strain.

Fault

Pipeline

(a) Before Fault Movement

Deformed Pipe

(b) After Fault Movement

Figure 1: Simplified Model for Pipeline Crossing Strike-Slip Fault

The final design may be based on selecting a combination of crossing angle and type of soil to

be used for controlled backfill. The strain induced at a fault crossing may also be decreased byincreasing the pipe wall thickness

As an alternate design for crossing faults which cannot be aligned properly or which

special trench and controlled backfill is not desired, the pipeline may be installed above

ground within the fault crossing zone of influence, and placed on concrete supported,

steel supports. The design must provide sufficient flexibility so that the pipeline can

sustain the fault displacement without exceeding the allowable stress and strain.

s


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6.0 LANDSLIDES AND MUD SLIDES

The type of soil and its stability must be determined in areas where it is planned to

install the pipeline on mountain slopes or any other areas that may be susceptible tolandslide or mudslides.

Detailed design of the pipeline must consider site specific static and dynamic analyses

for failure. A preliminary assessment of potential problem areas should be made. If theresults indicate a potential for landslides, detailed engineering design must consider site

specific static and dynamic analyses for failure. Some of the techniques for preliminaryassessment include the following:

Survey of case records of slope failures and collection of data from other sources

Field reconnaissance surveys by experienced personnel to identify slopes requiringdetailed analysis.

Use of photogrammetric or other surveying methods to identify slopes steeper thana specified gradient.

Preliminary analysis using conservative design parameters and analytic technique toidentify potentially unstable slope along the alignment so that detailed analysis can

be limited in number.

Unstable areas should be avoided by pipeline re-routing, if at all possible. Wherecrossing unstable areas is unavoidable, the following concepts may be considered for

risk mitigation.

Direct mitigation of the problem area, if economically feasible.

Orienting the pipeline so that the pipe axis is parallel to the direction of groundmovement Deeper burial of the pipe to a level below the unstable soil.

Modification to the construction zone and trench configuration.

Using heavier wall pipe for added strength.

Using tunneling or horizontal directional drilling (HDD) at the crossing to place thepipeline in stable ground underneath the unstable area (for use in any unstableground).

The most appropriate design solution to remedy the unsatisfactory conditions will vary

from slope to slope. This will depend not only on the geotechnical factors involved, butalso on civil/pipeline design and construction consideration and environmental,

drainage and erosion concerns.

Direct mitigation concepts are as follows:


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Grading to flatten slopes,

Provisions for subsurface drainage paths,

Soil densification and stabilization,

Replacement of susceptible soil,

Grouting or chemical stabilization,Slope buttressing or construction of retaining walls,

Installation of automatic shut-off valves on each side of the hazardous area, and

Close monitoring of the areas by aerial patrol and ground reconnaissance for earlyidentification and mitigation.

For most areas with potential landslide hazards, stabilization and/or repairs will not be

cost effective or practicable. For many areas, improving surface drainage and periodicmonitoring may be more effective.

7.0 KARST AREAS

The pipeline passes through terrain underlain by rock where karst processes create cave

caverns and sinkholes. These processes are the result of long term dissolution of solublecarbonate rock by slightly acid ground water and underground streams. The majorhazards to a pipeline in karst areas is the development of sinkholes which causes a loss

of support underneath the pipe so that it spans the extent of the sinkhole. If the diameterof the sinkhole is greater than the allowable span of the pipe, the pipe will be over

stressed and may fail.

Three major types of sinkholes may occur:

solution sinkholes,

cover-subsidence sinkholes, and

cover collapse sinkholes.

Solution sinkholes form in areas where carbonate rock is exposed at the ground surfaceor is thinly covered by permeable sediments. These sinkholes generally form by a

gradual downward movement of the ground surface and development of a depressionthat is typically bowl shaped and shallow. This type of sinkhole is not likely to damage

the pipeline since the pipe can settle to conform to the curve. In addition, such adepression should be detected by regular pipeline surveillance before it has developed

to an extent that it has caused damage to the pipeline.

Cover subsidence sinkholes occur in areas where carbonate rock is covered by relativelynon-cohesive and permeable unconsolidated sediments As the underlying carbonates

dissolve, individual sediment grains move downward in sequence to occupy spaceformerly occupied by carbonate rock. Sinkholes of this type are generally shallow, of

small diameter, and develop gradually. This type of sinkhole is not likely to damage the


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pipeline since the pipe can span small diameter holes. In addition, such a sinkholeshould be detected by regular pipeline surveillance and timely mitigation may be

undertaken.

Cover collapse sinkholes occur in areas where carbonate rock is overlain by sediments

with some degree of cohesion (e.g. sandy clays and clays). If a solution cavity in thecarbonate rock enlarges to such a size that the overlying material can no longer supportits own weight and collapses into the underlying cavity. Collapse is generally abrupt.

This type of sinkhole is most likely to cause damage to the pipeline.

Design of the pipeline to resist large, abrupt ground failures from cover collapsesinkholes is not practicable or feasible. It is recommended that the following approach

be taken:

make a geotechnical assessment to locate areas where collapse sinkholes areactively forming, and avoid these areas where possible,

locate any sinkholes that may be detected along the pipeline trench duringconstruction, and repair, and

regular surveillance for early detection during operations.

In order to assess the probability of pipeline failure due to formation of sinkholes, stressanalysis may be performed to determine the maximum allowable pipeline span lengths

to preclude overstressing the pipe steel. Such analysis should be based on pipediameter, pipe wall thickness, depth of pipeline burial in the area, and soil conditions.

The probability that an abrupt sinkhole of sufficient diameter to cause pipe failure

would form directly under the pipeline may be relatively low. This should bedetermined by a geotechnical assessment.

After construction, the Company should train its operation personnel to recognize the

early detection signs of possible sinkhole development, such as slumping or saggingobjects; structural failure or cracks in the ground surface; and/or unexpected ponding ofsurface waters. In the event that a sinkhole develops, appropriate site specific

mitigation measures should be undertaken.


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Typical Investigation Requirements for Seismic Design

1. Purpose of Geotechnical Investigation

To evaluate the pipeline route to determine geologic hazards to the pipeline,

including karst formations, fault crossings, ,slope stability and areas of potentialseismic induced ground failures such as landslides and liquefaction.

To provide recommendations regarding possible route refinements to avoidgeological hazards, or reduce geologic hazards; or design to accomadate the

hazards.

2. Karst Areas

Contractor shall identify areas along the pipeline route where existing sinkholes are

present and other areas which have a high potential for the formation of sinkholes.

Contractor shall also make recommendations for design to reduce the potential for

sinkhole.

2. Fault Crossings

Contractor shall identify active and potentially active faults crossed by the

pipeline and shall make design recommendations regarding the following:

Location of each fault along the pipeline route;

Width of the fault zone over which the surface displacement might occur;

Geometry of the fault relative to the pipeline;

Type, amount, and direction of fault movement that is likely to occur;

Recurrence interval for an appropriate seismic magnitude event along the

fault; and

Soils characteristics at the crossing and recommendations for soils design

values.

Bidder's proposal shall include a definition of the basic approach, types of

investigation, and proposed methods for identification and characterization of the

fault crossings.

3. Landslide Areas

Contractor shall identify areas along the pipeline route exposed to landslides

And shall make design recommendations regarding the following:


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Location and extent of each landslide hazard area along the pipeline route;

Recommendations for route alignment refinements to avoid or reduce the

effects of the landslide hazards;

Feasibility of stabilization of the landslide area;

Soils characteristics at the landslide area and recommendations for soils

design values.

Bidder's proposal shall include a definition of the basic approach, types of

investigation, and proposed methods for identification and characterization of the

landslide area.

4. Seismic Induced Ground Failures

Contractor shall identify areas along the pipeline route which have a high potential for

ground failures from slope instability, liquefaction, lateral spreading, andhydrocompaction resulting from seismic ground shaking. Contractor shall make

recommendations regarding the following:

Location and extent of each potential hazard area along the pipeline route;

Likelihood that ground failure hazards will occur in the hazard area;

Recommendations for route alignment refinements to avoid or reduce the

effects of the hazard;

Soils characteristics in the hazard areas and recommendations for soils

design values.

Bidder's proposal shall include a definition of the basic approach, the types of

investigation, and the proposed methods for identification and characterization of

the potential for seismic induced ground failures.

5. Final Report

The Contractor shall submit final reports detailing the work performed, observationsmade, results of laboratory and field tests, and the Contractor's recommendations for each

area of work, as applicable. Reports shall be submitted within 30 days of completion of

the geotechnical field investigations.


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Reports shall be in English, and using metric units of measurement. Terms used in the

final reports shall be in accordance with ASTM D653.

For each location investigated by the Contractor the following information shall be

presented:

description of location;

geomorphological characteristics, including but not limited to relative relief,

slope angle, and evidence of soil erosion;

soil mass characteristics if evident in areas of exposed soil;

geology, including tropical residual soil type;

hydrology, including drainage pattern, flow, and evidence of flooding;

vegetation, including broad type and percentage cover; and

dated photographs showing the typical features of the location.

anejo 5.1 especificaciones para construcción en Áreas propensas a terremotos dia- p gasoducto

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